Reconstruction with 3D-printed prostheses after type I + II + III internal hemipelvectomy: Finite element analysis and preliminary outcomes

Abstract

Background: Prosthetic reconstruction after type I + II+ III internal hemipelvectomy remains challenging due to the lack of osseointegration and presence of giant shear force at the sacroiliac joint. The purpose of this study was to evaluate the biomechanical properties of the novel 3D-printed, custom-made prosthesis with pedicle screw-rod system and sacral tray using finite element analysis. Methods: Four models that included one intact pelvis were established for validation. Forces of 500 N and 2,000 N were applied, respectively, to simulate static bipedal standing and the most loaded condition during a gait cycle. Biomechanical analysis was performed, and the results were compared; the preliminary outcomes of four patients were recorded. Results: For the reconstructed hemipelvis, stress was mainly concentrated on the sacral screws, bone-prosthesis interface, and upper endplate of the L5 vertebra. The optimization of the design with the sacral tray structure could decrease the peak stress of the sacral screws by 18.6%, while the maximal stress of the prosthesis increased by 60.7%. The addition of the lumbosacral pedicle-rod system further alleviated stress of the sacral screws and prosthesis by 30.2% and 19.4%, respectively. The site of peak stress was contemporaneously transferred to the connecting rods within an elastic range. In the retrospective clinical study, four patients who had undergone prosthetic reconstruction were included. During a follow-up of 16.6 ± 7.5 months, the walking ability was found preserved in all patients who are still alive and no prosthesis-related complications had occurred except for one hip dislocation. The Musculoskeletal Tumor Society (MSTS) score was found to be 19.5 ± 2.9. Conclusion: The novel reconstructive system yielded favorable biomechanical characteristics and demonstrated promising preliminary outcomes. The method can be used as a reference for reconstruction after type I + II + III hemipelvectomy.

Keywords: 3D-printed prosthesis; clinical outcomes; finite element analysis; hemipelvic reconstruction; sacroiliac joint.

FIGURE 1

3D model of the reconstructive system. (A) The anteroposterior view of the model. Green: the main body of the prosthesis. Pink: the artificial femoral head. Green arrow: the sacral tray structure. (B) The posterior aspect of the model. The screws being fixed on the prosthesis are defined as sacral screws (purple). Lumbosacral rods (blue) are fixed with five pedicle screws (short blue arrow).

FIGURE 2

Reconstructive models for FE analysis: (A) Model 1_B, (B) Model 2_B, (C) Model 3_B, and (D) Model 3_E.

FIGURE 3

The validation model of the normal pelvis. (A) The bilateral proximal femurs were restrained, and the load was applied to the L4 vertebra. (B) The distribution of the von Mises force. (C) The transmission of loading stress from the trunk (blue arrows). (D) The distribution of the force in the pelvic ring.

FIGURE 4

The von Mises force of the models. (A) Model 1_B. (B) Model 2_B. (C) The peak force of Model 2_B. (D) Model 3_B. (E) The peak force of Model 3_B at the locking site of the pedicle screw and the rod. (F) Model 3_E. (G) The peak force of Model 3_E at the pedicle screw–rod system of the healthy side.

FIGURE 5

The von Mises force of the sacral screws. The three horizontal screws were L5, S1, and S2 screws from top to bottom. (A) Model 1_B. (B) Model 2_B. (C) Model 3_B. (D) Model 3_E.

FIGURE 6

The von Mises force of the prosthesis and the force concentrated near the screw holes. (A) Model 1_B. (B) Model 2_B. (C) Model 3_B. (D) Model 3_E.

FIGURE 7

The patient (case 3) with the highest BMI was selected for FE analysis. (A) Preoperative magnetic resonance imaging (MRI) showed the involvement of the sacroiliac joint. (B) The surgery simulation that fitting the sacral tray onto the ventral sacrum. (C) The postoperative X-ray at the latest follow-up.